Adapting random access opportunities per synchronization signal block index for network energy savings

Abstract

Methods, systems, and devices for wireless communication are described. In some aspects, a network entity may allocate or configure multiple different quantities of random access channel (RACH) occasions and/or random access preambles, with each of the multiple different quantities of RACH occasions and/or random access preambles being associated with a respective synchronization signal block (SSB) index of a set of SSB indices. The network entity may allocate or configure a quantity of RACH occasions and/or random access preambles per SSB index based on a quantity of user equipments (UEs) served by the network entity in a direction associated with that SSB index. For example, the network entity may serve a coverage region associated with an SSB index and may allocate a quantity of RACH occasions and/or random access preambles for the SSB index based on a quantity of UEs within the coverage region.

What is claimed is: 
     
         1 . An apparatus for wireless communication at a user equipment (UE), comprising:
 one or more memories; and   one or more processors coupled with the one or more memories and configured to cause the UE to:
 receive information indicative of a plurality of quantities of random access channel (RACH) occasions associated with a plurality of synchronization signal block (SSB) indices, each quantity of RACH occasions of the plurality of quantities of RACH occasions associated with a respective SSB index of the plurality of SSB indices; and 
 transmit a message via a RACH occasion in accordance with the information. 
   
     
     
         2 . The apparatus of  claim 1 , the one or more processors, to receive the information, further configured to cause the UE to:
 receive the information via one or more fields of a RACH configuration information element.   
     
     
         3 . The apparatus of  claim 2 , wherein the one or more fields includes a single field, and wherein the single field includes an indication of each quantity of RACH occasions of the plurality of quantities of RACH occasions. 
     
     
         4 . The apparatus of  claim 3 , wherein a length of the single field is based at least in part on a quantity of the plurality of SSB indices. 
     
     
         5 . The apparatus of  claim 2 , wherein the one or more fields include a first field and a second field, and wherein the first field includes an indication of a baseline quantity of RACH occasions and the second field includes a plurality of deltas from the baseline quantity of RACH occasions, each quantity of RACH occasions of the plurality of quantities of RACH occasions associated with a respective delta, of the plurality of deltas, from the baseline quantity of RACH occasions. 
     
     
         6 . The apparatus of  claim 5 , wherein a length of the second field is based at least in part on a quantity of the plurality of SSB indices. 
     
     
         7 . The apparatus of  claim 1 , the one or more processors further configured to cause the UE to:
 map the plurality of SSB indices to RACH occasions in accordance with the information, wherein transmission of the message is based at least in part on the map of the plurality of SSB indices to the RACH occasions.   
     
     
         8 . The apparatus of  claim 7 , the one or more processors, to map the plurality of SSB indices to the RACH occasions, further configured to cause the UE to:
 map a first SSB index to a first subset of RACH occasions, wherein the first subset of RACH occasions includes a first quantity of RACH occasions, the first quantity of RACH occasions associated with the first SSB index in accordance with the information; and   map a second SSB index to a second subset of RACH occasions, wherein the second subset of RACH occasions includes a second quantity of RACH occasions, the second quantity of RACH occasions associated with the second SSB index in accordance with the information, and wherein the map of the second SSB index to the second subset of RACH occasions occurs after the map of the first SSB index to the first subset of RACH occasions in accordance with a mapping order.   
     
     
         9 . The apparatus of  claim 7 , the one or more processors, to map the plurality of SSB indices to the RACH occasions, further configured to cause the UE to:
 map a first SSB index to a first subset of RACH occasions, wherein the first subset of RACH occasions includes a largest quantity of RACH occasions of the plurality of quantities of RACH occasions; and   obtain a remainder of the first subset of RACH occasions based at least in part on a removal of one or more RACH occasions from the first subset of RACH occasions, wherein the remainder of the first subset of RACH occasions includes a first quantity of RACH occasions, the first quantity of RACH occasions associated with the first SSB index in accordance with the information.   
     
     
         10 . The apparatus of  claim 1 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via a paging indication.   
     
     
         11 . The apparatus of  claim 1 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via radio resource control (RRC) signaling.   
     
     
         12 . The apparatus of  claim 1 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via a system information block (SIB).   
     
     
         13 . The apparatus of  claim 1 , further comprising:
 an antenna array configured to cause the UE to:
 receive an indication of an SSB index of the plurality of SSB indices, wherein the SSB index is associated with a directional communication between the UE and a network entity; and 
   the one or more processors further configured to cause the UE to:
 select the RACH occasion from a quantity of RACH occasions associated with the SSB index. 
   
     
     
         14 . An apparatus for wireless communication at a user equipment (UE), comprising:
 one or more memories; and   one or more processors coupled with the one or more memories and configured to cause the UE to:
 receive information indicative of a plurality of quantities of random access preambles associated with a plurality of synchronization signal block (SSB) indices, each quantity of random access preambles of the plurality of quantities of random access preambles associated with a respective SSB index of the plurality of SSB indices; and 
 transmit, via a random access channel (RACH) occasion, a message that includes a random access preamble in accordance with the information. 
   
     
     
         15 . The apparatus of  claim 14 , the one or more processors, to receive the information, further configured to cause the UE to:
 receive the information via one or more fields of a RACH configuration information element.   
     
     
         16 . The apparatus of  claim 15 , wherein the one or more fields include a single field, and wherein the single field includes an indication of each quantity of random access preambles of the plurality of quantities of random access preambles. 
     
     
         17 . The apparatus of  claim 16 , wherein a length of the single field is based at least in part on a quantity of the plurality of SSB indices. 
     
     
         18 . The apparatus of  claim 15 , wherein the one or more fields include a first field and a second field, and wherein the first field includes an indication of a baseline quantity of random access preambles and the second field includes a plurality of deltas from the baseline quantity of random access preambles, each quantity of random access preambles of the plurality of quantities of random access preambles associated with a respective delta, of the plurality of deltas, from the baseline quantity of random access preambles. 
     
     
         19 . The apparatus of  claim 18 , wherein a length of the second field is based at least in part on a quantity of the plurality of SSB indices. 
     
     
         20 . The apparatus of  claim 14 , the one or more processors further configured to cause the UE to:
 select a first upper limit quantity of random access preambles per RACH occasion associated with a first SSB index of the plurality of SSB indices, the first upper limit quantity of random access preambles per RACH occasion equal to a product of a first quantity of random access preambles and a larger of a value of one or a quantity of SSB indices per RACH occasion, the first quantity of random access preambles associated with the first SSB index in accordance with the information; and   select a second upper limit quantity of random access preambles per RACH occasion associated with a second SSB index of the plurality of SSB indices, the second upper limit quantity of random access preambles per RACH occasion equal to a product of a second quantity of random access preambles and a larger of the value of one or the quantity of SSB indices per RACH occasion, the second quantity of random access preambles associated with the second SSB index in accordance with the information.   
     
     
         21 . The apparatus of  claim 14 , the one or more processors further configured to cause the UE to:
 select an upper limit quantity of random access preambles per RACH occasion in accordance with a product of a quantity of random access preambles and a larger of a value of one or a quantity of SSB indices per RACH occasion, wherein the quantity of random access preambles is a largest quantity of random access preambles of the plurality of quantities of random access preambles.   
     
     
         22 . The apparatus of  claim 21 , wherein the upper limit quantity of random access preambles per RACH occasion is used equally across the plurality of SSB indices. 
     
     
         23 . The apparatus of  claim 14 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via a paging indication.   
     
     
         24 . The apparatus of  claim 14 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via radio resource control (RRC) signaling.   
     
     
         25 . The apparatus of  claim 14 , the one or more processors further configured to cause the UE to:
 receive the information indicative of the plurality of quantities of RACH occasions associated with the plurality of SSB indices via a system information block (SIB).   
     
     
         26 . The apparatus of  claim 14 , further comprising:
 an antenna array configured to cause the UE to:
 receive an indication of an SSB index of the plurality of SSB indices, the SSB index associated with a directional communication between the UE and a network entity; and 
   the one or more processors further configured to cause the UE to:
 select the random access preamble from a quantity of random access preambles associated with the SSB index. 
   
     
     
         27 . An apparatus for wireless communication at a network entity, comprising:
 one or more memories; and   one or more processors coupled with the one or more memories and configured to cause the network entity to:
 output information indicative of a plurality of quantities of random access channel (RACH) occasions associated with a plurality of synchronization signal block (SSB) indices, each quantity of RACH occasions of the plurality of quantities of RACH occasions associated with a respective SSB index of the plurality of SSB indices; and 
 obtain one or more messages via one or more RACH occasions in accordance with the information. 
   
     
     
         28 . The apparatus of  claim 27 , further comprising an antenna array configured to cause the network entity to:
 output the information via one or more fields of a RACH configuration information element.   
     
     
         29 . An apparatus for wireless communication at a network entity, comprising:
 one or more memories; and   one or more processors coupled with the one or more memories and configured to cause the network entity to:
 output information indicative of a plurality of quantities of random access preambles associated with a plurality of synchronization signal block (SSB) indices, each quantity of random access preambles of the plurality of quantities of random access preambles associated with a respective SSB index of the plurality of SSB indices; and 
 obtain one or more messages via one or more random access channel (RACH) occasions, wherein each message of the one or more messages includes a respective random access preamble in accordance with the information. 
   
     
     
         30 . The apparatus of  claim 29 , further comprising an antenna array configured to cause the network entity to:
 output the information via one or more fields of a RACH configuration information element.